"We have had within thefe twenty years, five different menfurations of the Latitude of the earth, but we have hardly one of its Longitude. The apparent impoffibility of attaining to a fufficient degree of precifion, for want of our being able to find an arc large enough, parallel to the Equator, and fit for meafuring, has almoft made us defpair of this method. But if any place in the world feems to unite all the moft favourable cicumftances for measuring an arc in Longitude, it is in this part of Italy.

"A fignal placed on one of the fummits of the Appennine, from whence we may fee the Adriatic to the caft, and the Tufcan fea to the weft, cannot fail being perceived from one coaft to the other, provided it be of a fufficient magnitude. I fuppofe, for instance, that it may be feen from Ravenna or Rimini on one fide, and from Leghorn or Pifa on the other. Here then we have an arc of more than two degrees in Longitude, and eafy to be measured; but this is not all; for that diit ince may at least be doubled, of which the following is a proof; from the intermediary fummit of the Apennines, from whence we fee the two feas, one to the caft, the other to the west, the fight can be only bounded by the objc&is which terminate the horizon of the fea, and which are perceived on both fides. From this fame fummit then we ought neceffarily to fee in clear and ferene weather the fun rife from behind the mountains of Iftria and Croatia, and fet beneath thofe of Genoa.. Confequently a fudden flame of a fufficient volume, produced either by a mafs of gunpowder, as was propofed by me in 1735, and was actually carried into execution in 1740, or by a bomb of pafleboard placed on the fummit of the Apennine chofen for that purpose, might, in a fire night, be feen by two perfons appointed to obferve it, with each a regulator by him; the one at Monaco, or on the mountains of Genoa, the other on Cape Pola in Iftria, near Triefte. The difference of the hour in which each of them would perceive this artificial phenomenon, will give the difference of the Meridians of the two obfervatories, and the meafure of an arc nearly five degrees in Longitude.

"Though we should be able to affure ourselves of this difference of the hour but nearly within a fecond*, I am of opinion,

"I have found by experience, beneath the Equator, where the ftars r fe perpendicularly, and with very great rapidity, that it is not difficult, by taking feveral correfpondent heights, to inform one's felf with certainty of the inftant of noon, and above all of the mediation of a ftar nearly within a fecond; and experienced Obfervers wil. find, perhaps, that we may attain to a greater precifion. This half-fecond of

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nion, however, that it is poffible to attain a much greater degree of exactness, if we take all the necessary precautions, and especially

time anfwers to an arc of a degree of seven seconds and a half, which we may eltimate beneath the Equator, at one hundred and twenty toises, and which would be reduced again to eighty-four toifes, under a parallel of forty-four degrees and a half. Now an error of eighty-four toifes in an arc of five degrees, would not produce one of feventeen toifes to a degree, inftead of thirty-feur, which I have supposed; the following is the reafon of it: The difficulty of determining the hour exactly by correfpondent heights increases in an oblique sphere, where the apparent motion of the ftars is flower; and increases precifely in the fame proportion as the obliquity of the sphere, or in an inverse ratio to the cofinus of latitude. Thus, for example, beneath the parallel of fixty degrees, the radius of which is fubduple to that of the Equator, the fuppofed arc of feven feconds and a half would be by a moiety horter, and confequently would be only fixty toifes, instead of a hundred and twenty; but the difficulty of taking the hour exactly would be alfo as great again beneath this parallel, and inftead of an error of half a fecond, which we fuppofe might be made under the Equator, there would be under the parallel of fixty degrees an error of one fecond of time to be apprehended, which anfwers to fifteen feconds of a degree. Now an arc of fifteen feconds of a degree half as little, is equal in length to an arc of feven feconds and a half in a degree that is as large again. This would make us then an exact compenfation for it, and the error to which we should be exposed in the determination of the hour will be the fame under any parallel that we proceed upon: a circumftance which has not, that I know of, been remarked, or, at least, not explained, till now. It follows from thence, that the exactness of the aftronomical menfuration of an arc of Longitude may be equal in every country, and that it depends only on the length of the arc in toifes, whatever be the number of its degrees, If i were to confine myfelf then to the fuppofition of half a fecond, at which I eftimate, from my own experience, the error poffible to be committed in the determination of the hour, by correfpondent heights, beneath the Equator, this error would not be proportionally more than forty-two thirds for the parallel of forty-four degrees and a half, and would produce, like that of half a fecond beneath the Equator, only an error of an hundred and twenty toifes on an arc of five degrees; which would be no more than twenty-four toifes to a degree, inftead of thirty-four, which I have computed. But as the method which I have propofed requires two Obfervers, and it might happen, abfolutely fpeaking, that their errors, inftead of being none at all, or lefs, which I have not fuppofed them, might be as great as it is poffible for them to be, and that infead of compenfating one another, they might be doubled, though repeated and multiplied obfervations might be a remedy, morally fpeaking, for this accident; yet I have fuppofed the total error of the two Obfervers to be a whole fecond, even on taking a medium between their feveral obfervations. This fecond anfwers not to a hundred and feventy toifes on the parallel of forty-four degrees and a half, and yet it is on the fuppofition of that error, which furpaffes all the bounds of probability, that the er

ror

ally if the obfervations are often repeated) yet this error of a fecond in time, which is equivalent to fifteen feconds of a degree, amounts not in a parallel of forty-four degrees to one hundred and feventy toifes, which, being divided again among five degrees, would make only thirty-four toifes error to a degree; confequently, the measure of this arc of five degrees in Longitude, would afford as much or more precifion than our menfuration of three degrees of the Meridian, which I think I have proved we can answer for, to within very near forty toises.

"If Father Ximenes, the Reftorer of the Meridian of Florence, be commiffioned to make a map of Tuscany, and to meafure there an arc of the Meridian, his Geodefian measures, joined to thofe of the Fathers Maire and Bofcovick, will extend from one fea of Italy to the other, and go a great way towards taking the propofed menfuration in Longitude, which is fo well calculated to furnish us with new lights, refpecting the figure of the earth."

The remainder of the volume is taken up with what our ingenious Traveller obferved in other parts of Italy, viz. Bologna, Milan, Venice, Turin, and the Alps, which he croffed on his return to France.-We fhall conclude this article with the following juft encomium on M. de la Condamine, from the Tranflator's preface.

"As no perfon feems better formed by nature to make those enquiries, which the imperfection of all human wisdom ftill leaves but too much room for, fo nobody feems ever to have made them with more unremitted ardour and affiduity. Nor is his modefty, wherever he has occasion to mention himself, any ways inferior to his abilities. But candour, truth, and humility feem to have followed him wherever he went; and to these amiable qualities, no doubt, as well as to his uncommon share of learning, are to be attributed those great honours he met with from the eminent in every country through which he paffed. There is but one thing that I know of in which the bulk of mankind have reafon to be difpleafed with him; and this is, that when we fee fo many of them, particularly of our English Gentry, taking much longer tours, from which, nevertheless, they return empty, though poffeffed of all the neceffary means of improvement, M. de la Condamine, who fet out in an ill ftate of health, and unprovided of any fuch advantages, fhould

ror in a degree would be, and hardly, thirty-four toifes. It is evident. then, that the propofed menfuration in Longitude is fufceptible of as great, or even a greater, precifion, than that of three degrees of the Meridian."

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formifh out at once fuch an agreeable and inftructive narrative, as will for ever do honour to his memory."

In regard to the tranflation of this Memoir, we have given fuf

foort Decimens of it; and are forry that we can afford it no other proof of our approbation.

G

ACCOUNT of FOREIGN BOOKS.

Jean Jaques Rouleau, Citoyen de Geneve, a Chriftophe de Beaumont, Archevêque de Paris, Duc de St. Cloud, Pair de France, Commandeur de l'Ordre du St. Efprit, Provifeur de Sorbonne, &c. Or,

A Letter from J. J. Rouffeau, Citizen of Geneva, to Chriftopher de Beaumont, Archbishop of Paris, &c.--Occafioned by the Mandate of that Prelate, condemning the new Treatife on Education, entitled Emilius, &c. Amfterdam, printed for Rey.

TH

HE very zealous Ecclefiaftic, whofe name and dignities ferve to decorate the title-page of this performance, having officiously thundered out his anathemas against both Mr. Rouffeau and his book, that ingenious Writer enters into a warm and ferious expoftulation with him, on the fubject of his mandate; which, together with the fentence of the Parliament of Paris, he reprefents as cruel, unchriftian, and unjust.

On this occafion, he gives a flight sketch of thofe peculiarities, in his own life and conduct, which have brought him into his prefent difagreeable fituation. Before I proceed to my defence, fays he, "I cannot forbear refecting a little on the peculiarity of my deftiny: peculiar, indeed, to myself alone! I was born with fome fhare of natural genius; the public hath authorized me to make this boaft. I spent my youth, nevertheless, in an happy obfcurity, out of which I never attempted to emerge. Had I made fuch an attempt, indeed, it would have been as great a peculiarity, that, during the vivacity of youth, I should not have fucceeded, as that I fhould fucceed but too well in the fequel, when that vivacity fhould begin to decay. In this obfcurity, my Lord, instead of a fortune I always defpifed, and a name I have fince bought too dear, I poffeffed the only bleffings my heart was defirous of, thofe of tranquility and friendship. Thus, eafy in my mind, and happy in my friends, I drew near my fortieth year, when unluckily an academical question engaged my attention, and drew me into a profeffion for which nature never intended me. The unexpected fuccefs of my first

effay

ehay proved feductive. A numerous party of Oppofers started up against me, and, without understanding my arguments, anfwered them with a petulance that piqued me, and a degree of vanity that, perhaps, excited mine. I ftood up, of course, in my own defence; and, being urged from one difpute to another, found myfelf engaged in a career of controverfy, almost before I was aware. Thus I became an Author at a time of life when Authors ufually throw up their profeffion, and a man of letters even from my contempt for that character. From this time, I have been a Writer of fome little confequence with the public: but at this time, alas! my friends, and my repose, forfook me. My labour was all I got for my pains; and a little reputation was to make up for every thing clfe. If this be any indemnification to those who are ever abfent from themselves, it never was any to me.

"Had I placed, even for a moment, any hopes on fo frivolous a gratification, I fhould have been foon undeceived. In what a fluctuation hath the public opinion conftantly been, with regard to my abilities or character! Being at a distance, I was judged only by intereft or caprice; and for hardly two days together was I looked upon in the fame light. Sometimes I was a dark and gloomy Being; at others an angel of light. I have feen myfelf, within the space of one year, applauded, courted, entertained, and fought for, even at Court; and fpeedily after, infulted, threatned, hated, and abufed. Over night, affaffins lay in wait for me in the ftreets; and in the morning I was threatned with a lettre de cachet. The good and the evil came from almoft the fame fource; and both of them were the effect of a fong.

"I have written, it is true, on feveral fubjects, but always on the fame principles; I had always the fame fyftem of morals, the fame faith, the fame maxims, and, if you will, the fame opinions. Very different, however, have been the opinions that have paffed on my books, or rather on the Author of those books; because I have been judged rather from the fubject I have treated of, than from my fentiments on thofe fubjects. After the publication of my first Difcourfe*, I was faid to be a Writer fond of paradoxes, who amufed himself in proving things he did not believe. After my Letter on the French Mufic, I was called a profefied enemy to that nation, and was very near being treated as a confpirator and traitor: one would have thought, by the zeal fhewn on that occafion, that the fate of the French monarchy was attached to the reputation of their opera. After

In anfwer to the queftion, Whether the cultivation of the arts and fciences had contributed to the purity of manners ?

my